The present invention relates to a silica-based coating film on a substrate surface and a coating solution for the formation of a silica-based coating film on a substrate surface. More particularly, the invention relates to a silica-based coating film having a low dielectric constant formed on a substrate surface in the manufacturing process of various kinds of semiconductor devices to serve as a planarizing layer, interlayer insulating layer and the like as well as to a coating solution containing a specific hydrolysis-condensation product of a hydrolyzable silane compound for the formation of a silica-based coating film.
It is conventional in the manufacturing process of semiconductor devices that, when a planarizing layer or interlayer insulating layer has to be formed, a silica-based coating film is formed on the substrate surface to serve for the purpose. Several methods are utilized for the formation of such a silica-based coating film on a substrate surface including the chemical vapor-phase deposition (CVD) method, coating method by the use of a coating solution and others.
The CVD method, when applied to the formation of a silica-based coating film, is conducted by using a specialized apparatus in which silica optionally doped with phosphorus or boron is vapor-deposited to grow a silica-based coating film on the substrate surface. In the solution-coating method for the formation of a silica-based coating film, on the other hand, the surface of a substrate is coated with a coating solution containing a partial hydrolysis-condensation product of an alkoxy silane compound dissolved in an organic solvent followed by baking of the coating layer to complete the silica-based coating film, in which the hydrolysis-condensation reaction of the alkoxy silane compound in an organic solvent is performed usually in the presence of an acidic catalyst.
One of the serious problems in the electronic information-processing technology in recent years is that, along with the increasing trend of semiconductor devices toward a higher and higher degree of multiplication of multilayered pattern structure and fineness of patterning, a delay is caused in the signal transmission not to allow high velocity working of ULSIs. A large number of proposals have been made for a solution of this problem including an idea to employ a dielectric material of a low dielectric constant for the interlayer insulating layer.
For example, a proposal is made for an insulating film of silica doped with fluorine, referred to as an SiOF film hereinafter, as formed by the CVD method. One of the problems in the SiOF film is the expensiveness of the CVD apparatus therefor resulting in high costs. In addition, the SiOF film contains a Si—F linkage having high reactivity which reacts with water in the atmosphere to form an Si—OH linkage having an effect of increasing the dielectric constant of the film. Accordingly, the dielectric constant of SiOF films can rarely be lower than about 3.3.
In the solution-coating method for the formation of a silica-based coating film, proposals are made for the use of methyl polysiloxanes and hydrogen silsesquioxanes having a relatively low dielectric constant, such as a hydrolysis-condensation product of a dimethyl alkoxy silane and methyl silsesquioxane, as the film-forming constituent in the coating solution. The dielectric constant of the films consisting of a methyl polysiloxane and hydrogen silsesquioxane, however, can be about 2.8 and 3.3, respectively, at the lowest and a dielectric film having a dielectric constant lower than 2.8 can hardly be obtained. Accordingly, the solution-coating method by using these coating solutions cannot meet the requirements in the modern semiconductor devices for a lower and lower dielectric constant of the silica-based coating films.
It is a known technology that a poly(methylsilsesquioxane) powder as a filler for use in synthetic resins and rubbers and coating compositions are prepared from a polyalkoxy silane compound by conducting the hydrolysis-condensation reaction thereof in the presence of a basic catalyst (see, for example, Japanese Patent Kokai 54-72300 and 2-209927 for the powder and Japanese Patent Kokai 2-627 for the coating composition). No proposals have been made heretofore, however, on the application of such a technology to hydrolyze a polyalkoxy silane compound in the presence of a basic or alkaline catalyst for the preparation of a coating solution which can be used for the formation of a silica-based coating film on a substrate surface in the manufacturing process of semiconductor devices.
A method is disclosed in Japanese Patent Kokai 5-125187 for the preparation of a poly(organosilsesquioxane) having an extremely high molecular weight by promoting condensation of a low-degree hydrolysis-condensation product of a trialkoxy silane compound in the presence of an alkaline catalyst. Further, a proposal is made for the formation of a silica-based coating film having a low dielectric constant by using a coating solution obtained by conducting the hydrolysis treatment of an alkoxy silane compound in two steps including the first step in which the hydrolysis reaction is conducted in the presence of an alkaline catalyst to give a low-degree hydrolysis product which is further hydrolyzed in the second step in the presence of an acidic catalyst. The above described methods, however, are defective due to the low stability of the silica-based coating films obtained thereby and, even if the problem of stability is set aside, due to the dielectric constant of the coating films not low enough which is 3.8 at the lowest to be much higher than the target value of 2.5 desirable in the manufacture of semiconductor devices.